Aerofoil



May 13, 1924.

E. F. GALLAUDET AEROFOIL n Filed July 21. 1921 M1 m. mv

fief@ F. GAILUDET, 0F PRO ENE, RHODE ISLA :s

Application mcd July 21, 1921. Serial No. #$8,413.

To aZZ 'whom if may concern.'

Be it lmown that I, EnsoN F. G-Amnrmnr, a citizen of the United States,and a resident of the city of Providence, inthe count of Providence andState of Rhode Island have invented certain new and useful Imrovementsin erofoils, of which the fol- .owing is a specification.

This invention relates to aerofoils, and more particularly to taperedaerofoils or wings of airplanes.

Tapered aerofoils osscss certain distinct advantages over stralghtaerofoils. In the tirst place, since in thetapered aerofoils the liftingsurface is greatest at its base or inner end and smallest at the tip,the air forces impressed thereon in flight act nearer the bod` oi theairplane than in the case of a straig t aerofoil. Again, the thicknessof the aerofoil being greater at the base than at the tip, the spars andribs at and adjoining the base of the aerofoil may be made deeper, andconsequently lighter, than the similar parts of a straight aerofoil.Furthermore, the tapered form distributes the mass of the aerofoilstructure nearer the body of the airplane than in the case of a straightaerofoil, so that the inertia forces set up by the mass of the aerofoilitself act nearer to the airplane body and hence contribute less to thesum total of the forces the aerofoil mustl be designed to carry Ineneral, therefore, the tapered aerooil erm, by causing all the forcesimpressed on ordset up in the aerofoil to act nearer the bo straightaerofoil, is favorable ness and strength of the entire structure.

These advantages are, however, in large measure odset by the complexityof the tapered aerofol which, as heretofore constructed, is diiiicult ofdesign and stress anal sis and is poorly adapted for quantity prouction. No two ribs in a/,tapered aerooil are the same. Even where allof the ribs are made tothe same contour the dimensions will be differentfor each one, and, in case the ribs are not all of the same contour, thedesign is different for cach and both design and construction becomevery laborious. Moreover, the spars, if parallel, cannot pass throu hthe ribs with any uniformity, as they o in a straight aerofoil, and.conversely, if they pass through the ribs at the same relativelpointstherein, they will not be parallel. Hence, es the tol the lightof theairplane than in the case of a base of the aerofoil is seldom differentmembers for contour at the suitable for the tip, attaching the ribs toquired at every rib.

By my present invention I have obviated all of the above disadvantages,while at the same time realizing aerofoil forms of the highesteliciency.

My new tapered aerofoil is characterized y a maximum or base sectionwhich is bounded by intersecting upper and 'lower contour lines,variable at will and so laid out as to give to the aerofoil the contourbest adapted to the particular purpose in view, and, from base to tip,by successively reduced sections which are established by successivelyreducing the distance between the upper and lower contour lines of thebase section, moving the lines towards each other without changingeither theirangular relationship or their curvature. The front and rearintersections of the two lines form, respectively, the entering andtrailing edges of each section.

The aerofoil may be defined as formed by two curved surfaces in whichthe generating lines describing the two surfaces respectively areinclined toward one another at an angle equal to the angle of taper.Where the angle of inclination ofthese generating lines remains constantthroughout, the aerofoil will have a uniform taper from end to end. Inthe event that uniform taper is not desired, however, the angle,starting from a zero angle if desired, may `be changed from time totime, thus giving to the aerofoil different degrees oi ta'per throughdifferent portions of its length. i

In all cases, the aerofoil will have a thick section at the base, a thintip section, and will both sweep back along its entering and forwardalong its trailing edge. At two points in each section, one near theentering edge and the other 'towards the trailing ed e convenient forthe location of the spars, te thickness of the aerofoil, or the verticaldistance between its up er and lower contourlines,is the same, an thesepoints are constant in distance apart and position througlr out thelength of the aerofoil. Consequently, by placing the spars at thesepoints two spurs which are exactly alike can be used and will, or may',be parallel oneto the other. Moreover.y since the curvature of thesectional contour lines of any given aerofoil the spars will be rellOlil

example at a dihedral angle relative to the ,front spar so as to give aso-called washout to the aerofoil.

The new aerofoil is easy to design, `analyze, and construct, eithersingly or in uantity production, and can bev made of t e requiredstrength with a minimum weight of material.

'l e invention will be understood by reference to the accompanyingdrawings, 1nvl by Letters Patent, is

which- Figure 1 is an end view of an aerofoil embodying my invention,showing the upper and lower contour lines at the base, tip, and .twointermediate points in the length of the aerofoil; Fig. 2 is a section,more or less diaammatic, on either of the two lines 2 2 of ig. 1; Fig. 3is a'view, similar to Fig. 1, of a modified form of aerofoil adapted fora diierent type of airplane; and Fig. ,e is a section, one either of thetwo lines 4 4, of the modified aerofoil shown in Fig. 3.

As illustrated in Figs. 1 and 2, the u per and lower contour lines w bof the inner ase section of the aerofoil are laid out from a base ordatum line A A, which is here coincident with the chord line, inoutwardly con- Vex curves which produce an aerofoil, relatively thin andwitha low head resistance secured at a small sacrifice in lift, adapted'duces a gf chord line to small machines of great speed andmoderatelifting capacity. In this aerofoil the outer sections are shownas established by movin the contour lines a b towards each other ysuccessively equal `amounts for successively equal distances, the upperline however-at amore rapid rate than the lower line. Hence, the lines ab', a b", and a b", show the contour of sections at onethird of thelengthof the aerofoil from its base, at two-thirds of its length fromits base, and atth tip, respectively; and the spars, located at the sparlpositions represented by the fore `and aft section lines 2 2 in Fig. 1,will be exactly alike, will be parallel, and will have in side elevationthe uniform taper shown in Fig. 2.

The'modied form of aerofoil illustrated in Figs. 3 and 4 is oneparticularly adapted for 'lar e machines of moderate speed and highIifting capacity'. The convexedly curved contour line a! andvconv'exl/-com vcavely-convexly', .or compound, curve contour vline bgive it curved on its upper surface Iand with a hollow camber on ltsvlower surface'.which-pro-` B B separate` from the To establish the outersections datum line.

a thick section heavilyy aeree of this'aeroioil, the upper and lowercontour lines of its base section are brought towards each other bysteps not proportioned to dis-v tance from the base. Thus, the contourlines a b show the section midway of the length 1. ln an airplane aframed and enclosed structure which is tapered through a portion atleast of its length and which at the base of such tapered portion has asection bounded by two contour lines both curved convexly outward andintersecting each other at opposite points in the section and from thebase to the tip of the tapered portion has successively reduced sectionsbounded by contour lines determined by successively moving nearer and'nearer together the two said curved lines without chan e either in theircurvature or in the angu ar relationship of one to the other.

2. A tapered aerofoil having' a base section bounded byv suitably curvedupper and lower contour-lines which intersect fore and aft to form itsentering and trailing edges and give to the section equal depth' at twooints lone fore and one aft suitable for the ocation of spare andthrough its tapered outer portion having successively reduced sectionsestablished by ysuccessively bringing nearer and nearer together the twocontour lines of the `base section' without change in the angularrelationshipv of one to t e other; f A tapered aerofoil having a basesecv tion bounded by suitably curved upper and lower contour lines whichintersect fore and aft to form its entering andv trailing edges and giveto the -section equal depth at two oints one fore and ,theother aftsuitable er the location of sparsand from. base tov tip) havingsuccessively reduced sections esta lished by moving thecontour lines ofthe -base sectionv towards each other by successively equal amounts forisuccessively equal distances without change in theai-v .gularrelationship of one to .the other.

the outer half atleast of`- its len th and which has a, base'sectionbounded ablyscu'rved ,upper and, lower ccntourflines intersectingeachother `foreand kaft tojform the entering and trailing'edges andthrouh its tapered outer portion hasfseccessivy 4f. An aerofoil lwhich `istapered through y suit-- Luanne v reduced sections established bysuccessively bringing nearer and nearer together. the two contour linesof the base section, the upper contour line being moved at a more rapidrate than the lower, without change in the angular relationship of oneto the other.

5. A tapered aerofoil which has a thick base section and a thin tipsection, which throughout the outer portion at least of its len h sweepsboth back along its entering an forward along its trailing edge, andwhich in each section from base to tip is of like thickness at twopoints one fore and the' other aft -vwhich are vconstant in distanceapart throughout the length of the aerooil.

6.' A tapered aerofoil having parallel longitudinal sections fore and at of the ceuter of .pressure respectively in which at each transversesection lines perpendicular 2o 'to the chord line are of the samelength.

7. A tapered aerofoil having parallel fore and aft spar positions whichare of the' same depth at each transverse section of the aerofoil.

EDSON- F. GALLAUDET.

